1. Field of the Invention
The present invention relates to a method for dynamically adjusting a gain of parametric equalizer according to an input signal, a dynamic parametric equalizer employing the same and a dynamic parametric equalizer system employing the same, and more particularly to a method, a dynamic parametric equalizer and a dynamic parametric equalizer system wherein a gain of parametric equalizer is dynamically adjusted according to a level of an input digital audio signal.
2. Description of the Related Art
Parametric equalizer is an equalizer capable of configuring parameters such as a band and a gain according to user's preference. The parametric equalizer constitutes an audio tuning circuit included in a digital audio playback device in order to match a digital audio signal to a playback capability of a speaker. For instance, the parametric equalizer is used to tune a characteristic of a digital audio signal in order to match a characteristic of a speaker built into a digital television. When a bass playback capability of the speaker built into the digital television is poor, bass playback may be appropriately carried out without any distortion when the characteristic of the digital audio signal is properly tuned using the parametric equalizer. That is, the parametric equalizer is used to generate a signal suitable for the playback capability of the speaker. The parametric equalizer comprises digital filters which are designed considering the playback capability of the speaker at the time of designing the digital audio playback device.
FIG. 1A is a graph exemplifying a transfer function of a conventional parametric equalizer. As shown in FIG. 1A, the conventional parametric equalizer amplifies a signal within a bandwidth Q about a center frequency fcenter according to a preset gain G.
FIG. 1B is a graph exemplifying a transfer function of another conventional parametric equalizer. As shown in FIG. 1B, the conventional parametric equalizer amplifies a signal with a frequency lower than a cut-off frequency fc according to a preset gain G.
FIG. 1C is a graph exemplifying a transfer function of yet another conventional parametric equalizer. As shown in FIG. 1C, the conventional parametric equalizer amplifies a signal with a frequency higher than a cut-off frequency fc according to a preset gain G.
As shown in FIGS. 1A through 1C, the conventional parametric equalizer amplifies a signal of a predetermined band according to preset parameters. When a level of the signal inputted to the parametric equalizer is relatively small, the amplification can be performed without any distortion. However, when the level of the signal inputted to the parametric equalizer is relatively large, the amplification may result in a clipping of the signal.
In order to prevent the clipping, the gain of the parametric equalizer should be adjusted in real time according to the level of the input signal. That is, when the level of the input signal is low such that the clipping should not occur, the input signal should be amplified by the preset gain G. When the level of the input signal is high such that the clipping should occur, the input signal should be amplified by a gain lower than the preset gain G to prevent the clipping.
As shown in FIGS. 1A through 1C, the parametric equalizer is embodied by a filter. For instance, when the parametric equalizer is embodied by a second order IIR (Infinite Impulse Response) filter, the transfer function of the parametric equalizer is represented by equation 1 below.
                              H          ⁡                      (            z            )                          =                                            b              0                        +                                          b                1                            ⁢                              z                                  -                  1                                                      +                                          b                2                            ⁢                              z                                  -                  2                                                                          1            +                                          a                1                            ⁢                              z                                  -                  1                                                      +                                          a                2                            ⁢                              z                                  -                  2                                                                                        [                  Equation          ⁢                                          ⁢          1                ]            
In order to prevent the clipping, the gain of the parametric equalizer should be dynamically varied according to the level of the input signal. That is, the parameters of the filter constituting the parametric equalizer should be changed in real time. Since the parameters of the filter are defined by coefficients of Equation 1, coefficients a1, a2, b0, b1 and b2 should be calculated every time the gain is changed.
Since the calculation of the coefficients of the IIR filter in real time is very complex and requires high performance arithmetic hardware, the constitution of the hardware becomes more complex and the manufacturing cost thereof rises.